Conventionally, a vehicle traveling with its accelerator released (i.e., in an accelerator released state, or in an accelerator OFF state) stops fuel supply to an internal combustion engine, when the rotation number of the engine per unit time (engine rotation speed) is high, and provides a required amount of fuel to the engine when the engine rotation speed is low, for maintaining an idle state of the engine. The above fuel supply scheme is designated as fuel cutoff.
It is proposed by JP 2005-337229A (US 2007/0213920 A1), for example, to perform a driving diagnosis for determining a degree of fuel-efficient driving, based on measurement of travel time of the vehicle in the accelerator OFF and coasting (travel by inertia) state during a deceleration time of the vehicle.
It is also proposed by JP 2010-209834A (US 2010/0235038 A1), for example, to measure a time length after a deceleration of a subject vehicle under a set speed while a travel speed of the vehicle is under the set speed. In this proposal, a time of the travel of the vehicle with its accelerator position being released (i.e., traveling in the accelerator OFF state) is designated as a required stopping time.
As one of operation states of the vehicle, the subject vehicle travels a road including a downward slope, for a period of time (i) from a starting time of a deceleration by putting the accelerator in the accelerator OFF state, (ii) to a stop of the subject vehicle at a target stop position, without putting the accelerator in an accelerator ON state.
In such a situation, the conventional driving diagnosis technique, as exemplified in FIG. 6, after starting (time t21) a deceleration by putting the accelerator in an OFF state (i.e., throttle opening is zero), measurement of lapse time T1 is started at a time (time t22) when the travel speed of the subject vehicle falls down below a set speed V2. Then, if the road traveled by the subject vehicle turns downward (time t23), to lead to acceleration of the subject vehicle to have the travel speed exceeding the set speed V2 (time t24), the conventional driving diagnosis technique typically ends the measurement of the lapse time (T1 in FIG. 6). Then, the deceleration of the subject vehicle is re-started to have the travel speed of the subject vehicle fall down under the set speed V2 (time t25) after ending the travel on the downward road, and measurement of the lapse time (T2 in FIG. 6) is newly started, and the newly-started measurement of the lapse time T2 continues until the subject vehicle stops (time t26).
In this example, even when the vehicle continuously accelerates and decelerates during coasting (travel by inertia), the conventional driving diagnosis technique measures the required stopping time twice in one continuance of such coasting, thereby deteriorating measurement accuracy of required stopping time T and a degree of driving fuel-efficiency.